That idea is biased against the Extraverts. What you're implying is that while Introverts have the ability to understand both themselves and the outerworld, Extraverts understand the outer world okay, but some will never really have a grasp on introspection. Why is that?

Fine.... introverts may or may not want to understand their external world. Better?

Yes, but introverts are forced to face and deal with the external world a great deal more than the extravert is forced to be introspective. Hence in average examples of both, the introvert is perhaps slightly more likely to be well-rounded in that regard.